Installation for producing objects by thermoforming pellets of thermoplastic material

ABSTRACT

The installation for manufacturing objects such as receptacles by thermoforming pellets of thermoplastic material includes conveyor means for conveying the pellets through the various stations in the installation, said stations including a heating station and a thermoforming station. The conveyor means comprise conveyor elements ( 46 ) defining cells ( 48 ) which are open upwards and downwards, and each of which is suitable for containing one pellet ( 12 ) while the entire top and bottom faces of the pellet remain unobstructed, means for depositing the pellets in the cells, drive means for driving the conveyor elements through the heating station, and transfer means ( 20 ) for transferring the heated pellets to the thermoforming station. The heating station includes bottom heater means ( 52 ) that co-operate with a support for the pellets while said conveyor elements are being driven through the heating station.

The present invention relates to an installation for manufacturingobjects such as receptacles by thermoforming pellets of thermoplasticmaterial, said installation including conveyor means for conveying thepellets through the various stations in the installation, said stationsincluding a heating station for heating said pellets, which stationincludes bottom heater means and top heater means, and a thermoformingstation for plastically deforming the heated pellets by stretching them.

An installation of that type is known from French Patent No. 2 766 123which explains the advantages related to using pellets of thermoplasticmaterial rather than a continuous strip for thermoforming objects suchas receptacles, those advantages relating in particular to the fact thatwastage is avoided or considerably reduced.

It is even possible to make provision for the edges of the pellets todefine the edges of the thermoformed objects, without it beingnecessary, after thermoforming, to perform any additional operation forrectifying said edges.

However, that generally requires the edges of the pellets to be deformedeither after the thermoforming operations or during said operations. Inorder to achieve such deformation satisfactorily, it is desirable forthe entire surface of each of the pellets to be heated to thethermoforming temperature in the heating station.

Unfortunately, in FR 2 766 123, the pellets are carried through theheating station by supports having rims on which the edges of thepellets rest. As a result, the zones of the pellets that are supportedby the rims cannot be heated correctly, at least as regards the heatingperformed by the bottom heater means.

An object of the invention is to improve that state of the art furtherby making it possible to heat the pellets better.

This object is achieved by the fact that the conveyor means compriseconveyor elements defining cells which are open upwards and downwards,and each of which is suitable for containing one pellet while the entiretop and bottom faces of the pellet remain unobstructed, means fordepositing the pellets in the cells, drive means for driving theconveyor elements through the heating station between the bottom heatermeans and the top heater means, and transfer means for transferring theheated pellets to the thermoforming station, and by the fact that thebottom heater means co-operate with a support for the pellets while saidconveyor elements are being driven through the heating station.

As explained below, the support may, for example, be constituteddirectly by a bottom heater plate, or else it may be constituted by abelt which is made of a heat-conducting material and which transmits theheat generated by the bottom heater means to the pellets while beingdriven in a manner such as to be synchronized with the conveyorelements. In either case, the support is in thermal contact with thebottom heater means, via heat transfer, or because it is constituted bythe surface of a heater plate.

The top and bottom faces of the pellets are entirely unobstructed whenthe pellets are disposed in the cells, thereby making it possible forthe entire bottom face to be exposed to the bottom heater means and forthe entire top face to be exposed to the top heater means. The heatermeans may be constituted by a heater plate, or else by radiating heatermeans.

By being driven through the heating station, the conveyor elements pushor pull the pellets with them so that they are also driven through saidstation, inside which the support for the pellets transmits the heatgenerated by the bottom heater means to said pellets. As a result, theheating of the pellets is of extremely good quality. In addition, thebottom faces of the pellets can rest on the surface of the support notonly while the pellets are stopped in said installation, but also whilesaid pellets are advancing through one step, the drive generally beingstepwise.

In a first embodiment, the bottom heater means comprise a bottom heaterplate, and said plate constitutes a support for the pellets while theconveyor elements are being driven through the heating station.

Advantageously, the installation includes a cold support plate which isdisposed on one side of the bottom heater plate, and whose surfaceextends in the same horizontal plane as the surface of said heaterplate, the bottom heater plate and the cold support plate being mountedto move sideways between a first position in which the bottom heaterplate is suitable for supporting the pellets and a second position inwhich the cold support plate is suitable for supporting the pellets.

When the installation is in operation, with the heater means having beenbrought up to temperature, it can be necessary to stop it momentarily inorder to remove defective pellets or else to reload the inlet of themachine with pellets. Depending on the time for which the installationis stopped, it can be desirable to prevent the pellets present in theheating station from remaining in contact with the bottom heater platethat might heat them excessively and damage them. By means of theabove-mentioned provisions, it suffices, during a stop stage, to movethe bottom heater plate and the cold support plate sideways so that thepellets are supported by said support plate.

When the top heater means are radiating heater means, it can suffice,during a stop stage, to stop powering the heater means so that theycease to heat the pellets.

However, advantageously, said top heater means are also suitable forbeing moved sideways with the bottom heater plate and the cold supportplate so as to avoid exposing the pellets to said top heater means whilethe installation is at a stop.

Advantageously, the installation includes a cold top plate which isdisposed above the cold support plate, and said cold top plate, and thetop heater means are mounted to move sideways between a first positionin which the top heater means are situated above the pellets and asecond position in which the cold top plate is situated above thepellets.

The cold top plate makes it possible, when the pellets are between thetwo cold plates while the installation is at a stop, not only to preventthe temperature of said pellets from rising, but also to protect themagainst any dust.

The cold plates may be made of an insulating material so as to preventthe heat generated by the heater means from diffusing through saidplates. They can optionally be refrigerated.

Advantageously, the top heater means comprise a top heater plate thatpresents a bottom surface suitable for being in contact with the topfaces of the pellets.

This contact facilitates heating of the pellets, whose two faces areentirely uncovered by the conveyor means, and are in contact with thebottom and the top heater means. The top heater plate may presentprojecting heater surfaces which, during a heating stage, penetrate intothe cells of the conveyor elements so as to come into contact with thetop faces of the pellets.

However, it is advantageous for said top heater plate to be providedwith a bottom surface that is plane, and for provision to be made forthe top faces to stand proud (i.e. to project beyond) the conveyorelements. The top heater plate may be movable vertically so as to moveaway form the pellets during a drive stage.

In a second embodiment, the installation includes a bottom belt made ofa heat-conducting material, and means for transmitting the heatgenerated by the bottom heater means to said belt. The bottom beltconstitutes the support for the pellets which rest on the top surface ofsaid belt. The bottom belt is driven through the heating station in amanner synchronized with the conveyor elements.

Advantageously, the installation includes a top belt made of aheat-conducting material, and means for transmitting the heat generatedby the top heater means to said belt. The bottom surface of said belt issuitable for being in contact with the top faces of the pellets, and, inaddition, the top belt is driven through the heating station in a mannersuch that it is synchronized with the conveyor elements.

Advantageously, the conveyor elements are constituted by conveyor slats.

Said slats advantageously present a thickness at the most substantiallyequal to the thickness presented by the pellets before they arethermoformed.

Said slats may be spaced slightly apart from the bottom heater plate(for example, it suffices for the spacing to be a few tenths of amillimeter), and also spaced apart slightly from the surface of the topheater plate during a heating stage.

For example, with the installation being organized to operate withpellets of a given thickness, the thickness of the conveyor slats issmaller than said given thickness by a value lying the range a fewtenths of a millimeter to 1 to 2 millimeters.

Advantageously, each cell is defined between an upstream conveyor slatand a downstream conveyor slat disposed in succession in the directionin which the pellets are conveyed.

Thus, advantageously, the outline of each conveyor slat is provided witha downstream concave edge and with an upstream concave edge that aremutually aligned in the conveying direction in which the pellets areconveyed, the downstream concave edge of a first slat being suitable fordefining a cell with the upstream concave edge of a second slat disposeddownstream from said first slat.

This facilitates disposing the pellets in the cells since a pellet canbe disposed between the facing concave edges of two slats, before saidslats are disposed one against the other in order to close the cellformed by said two concave edges against the edge of the slat.

In another variant, each slat can be in the form of one piece providedwith whole cells.

The invention will be better understood and its advantages will appearmore clearly on reading the following detailed description of anembodiment shown by way of non-limiting example.

The description refers to the accompanying drawings, in which:

FIG. 1 is an overall view of an installation of the invention includinga first embodiment of the heating station;

FIG. 2 is a cross-section view of FIG. 1, showing the heating station;

FIG. 3 shows how the conveyor slats move in the installation;

FIGS. 4 and 5 are diagrammatic vertical section views in thethermoforming station;

FIG. 6 is a diagrammatic perspective view of the bottom tool of thethermoforming station; and

FIG. 7 is a view seen looking along arrow VII of FIG. 6;

FIG. 8 is an overall view of an installation of the invention includinga second embodiment of the heating station;

FIG. 9 is a diagrammatic perspective view of the upstream portion of thethermoforming station;

FIG. 10 a is a diagrammatic view in a vertical plane of the bottomheater plate, of the support rods, and of the bottom belt while theinstallation is stopped; and

FIG. 10 b is a diagrammatic view in a vertical plane of the bottomheater plate, of the support rods and of the bottom belt while theinstallation is operating.

The installation shown in FIG. 1 includes a heating station 10 forheating pellets 12 of thermoplastic material, means for driving thepellets through the heating station to the outlet of said station, and athermoforming station 14 in which the hot pellets are deformedplastically to form objects such as receptacles 16.

The hot pellets are transferred from the outlet of the heating stationto the thermoforming station by transfer means 18. Said transfer meanscomprise pick-up means, e.g. a suction-cup arm 20 suitable for pickingup the hot pellets using suction and substantially without cooling them,and for conveying the pellets to the thermoforming station. For example,the suction-cup arm is controlled in a cycle comprising a verticalmovement for picking up the pellets and for raising them using suction,then a horizontal movement on a carriage until the suction-cup arm comesabove the bottom tool 22 of the thermoforming station 14, following bylowering inside said station, and interrupting the suction so that thepellet is disposed on the bottom tool 22, and then return to thestarting position.

In this example, said bottom tool 22 is a thermoforming countermold thatmovably receives a thermoforming piston 24 which, when the thermoformingmold 26 is closed against the countermold, moves in translation todeform the pellet 12 and to bring the material thereof into the chamberin the mold 26, the pellet being pressed against the wall of said moldby air injection. In the example shown, the receptacles are thermoformedupwards, the mold being the top tool of the thermoforming station. Inaddition, in the example shown, each of the thermoformed receptacles isprovided with a neck 16A which forms an undercut, and the mold 26 ismade up of a plurality of portions 26A and 26B that can be moved apartfor unmolding purposes.

At the outlet of the thermoforming station, the receptacle that has justbeen thermoformed is picked up by means of tongs 33A. For example, saidtongs equip the free end of a retractable arm 33 which is deployed inorder to pick up the receptacle in the thermoforming station, and whichis retracted in order to move it away therefrom.

The arm 33 is mounted on a pivotally mounted support 34, thereby makingit possible to turn the receptacle the right way up so that its neck isdisposed upwards after it is moved away from the thermoforming station.The righted receptacle, still carried by the arm 33, is disposed in thefilling station 40. It can be taken up by a bottom support 36 which ismovable along the sides of a rectangle as indicated by arrows F36 so asto be placed under the filled receptacle, so as to support said filledreceptacle, and so as to bring it by moving it horizontally into astation 42 for fitting and sealing a lid or a cap. At the outlet of thisstation, the receptacle is taken up by another arm 43 equipped withtongs, which arm places it on the final conveyor enabling it to beremoved from the installation and to be packaged.

As can be better understood from FIG. 3, the conveyor means compriseconveyor elements constituted by conveyor slats 46 which define cells 8that are totally open both upwards and downwards. One pellet 12 can bedisposed in each cell, without being retained either upwards ordownwards. In order to make the drawings clearer, the conveyor slats inFIG. 1 are shown in section in the plane that contains the cell diameterthat is parallel to the direction of advance F.

In this example, each cell, such as the cell 48C, is defined between anupstream conveyor slat 46A and a downstream conveyor slat 46B that aredisposed in succession in the direction F in which the pellets areconveyed. More precisely, it can be seen that each conveyor slatpresents at least one downstream concave edge 48A and at least oneupstream concave edge 48B, respectively disposed on the downstream sideand on the upstream side of the slat in the direction F.

It can be seen that, when two successive slats are disposed such thatthe downstream side of the upstream slat is touching the upstream sideof the downstream slat, the downstream concave edge of the upstream slatand the upstream concave edge of the downstream slat are disposed facingeach other so as together to define a closed cell in which a pellet 12can be disposed.

Said edges then form a continuous boundary for said cell, e.g. in theform of a circle.

In the example shown, the installation makes it possible to thermoformtwo receptacles in each thermoforming step. That is why it works fromtwo stacks of disks 12 and 12′ disposed side by side in the transversedirection S of the installation.

Naturally, it could also work from more than two stacks of disks so asto thermoform receptacles over more than two rows, or indeed work from asingle stack.

In the description below, operation of the installation is describedwith reference to the elements thereof that act on the disks in one ofsuch stacks.

Thus, FIG. 1 shows that the installation includes an inlet table 50whose surface 50A extends in the same horizontal plane as the surface52A of the bottom heater plate 52.

The conveyor means comprise means for bringing a conveyor slat onto theinlet table into a waiting position in which the downstream concave edgeof said slat is facing the stack. The slat 46C of FIGS. 1 and 3 is insaid waiting position. The conveyor means further comprise means formoving said slat downstream, in the direction F, so that the downstreamconcave edge 48A of said slat co-operates with the bottom pellet 12 inthe stack so as to drive said pellet downstream, at least until saidslat reaches an intermediate position in which the upstream concave edgeof said slat is in front of the stack.

In FIG. 3, slat 46D is in said intermediate position. At the precedingstep, it was in the position occupied by slat 46C and it has been movedso that its downstream side comes against the upstream side of the slat46E disposed immediately downstream from it. Similarly, it can beunderstood that the slat 46C can be moved so as to take up the bottompellets 12A and 12′A of the two stacks via its two downstream concaveedges 48A and 48′A, before pushing said pellets against the upstreamconcave edges 48B and 48′B of the slat 46D. When said slat 46C hasreached its intermediate position, other pellets can come into contactwith the inlet table, and another slat can take up the waiting position.

The drive means advantageously comprise a drive member that is movablein reciprocating manner between a first position in which it is suitablefor co-operating with a slat in the waiting position, and a secondposition in which it places said slat into its intermediate position. Inthe example shown, said drive member is constituted by an actuator 54which, when a slat is on the inlet table, in its waiting position, canpush it until it takes up its intermediate position, and can thenretract so as to wait for another slat to come into its waitingposition. When a slat reaches its intermediate position, it pushes theslats disposed in front of it downstream. In this way, the pelletscontained in the cells defined between the slats are conveyed stepwisethrough the installation.

The pellets contained in the cells defined between the slats aresupported by the inlet table 50 until they reach the heating station 10.Whereupon, the pellets are supported by the surface of the heater plate52. FIG. 2 shows a slat 46 and two pellets 12, 12′ disposed on the topfaces 52A and 52′A of respective ones of the two bottom heater plates 52and 52′.

The heater tools enable pellets coming from both stacks to be heatedsimultaneously. For reasons of simplicity, only those heater tools whichare situated on the right of FIG. 2 are described below, the tools ofthe left being identical and being designated by like references withthe prime sign “′”.

It can thus be seen that the installation includes a cold support plate56 which is disposed on one side of the bottom heater plate 52. Its topsurface 56A extends in the same horizontal plane as the top surface 52Aof said heater plate. In FIG. 2, the bottom heater plate 52 and the coldsupport plate 56 are in their first position in which the bottom heaterplate is supporting the pellet 12. When the installation stops, they canbe moved together sideways in the direction S that is transverse to thedirection F, so as to take up a second position in which it is thesupport plate 56 that supports the pellet 12.

In the example shown, the plates 52 and 56 are carried by the samebottom deck 58 relative to which their positions can be adjusted so thattheir surfaces 52A and 56A are strictly in alignment with each other.The deck is mounted on a carriage 60 which can be moved in reciprocatingmanner by an actuator 61, so that the plates 52 and 56 can take up theabove-mentioned first and second positions.

The plates 52′ and 56′ are mounted on a deck 58′ which is carried by thesame carriage 60.

Similarly, the heater tools on the right of FIG. 2 comprise a top heaterplate 62 and a top cold plate 66 which is disposed above the coldsupport plate 56. The plates 62 and 66 can be moved sideways in thedirection S between a first position (shown in FIG. 2) in which the topheater plate 62 is disposed above a pellet 12, and a second position inwhich the top cold plate is situated above said pellet.

The plates 62 and 66 are supported by a common top deck 68 which isitself carried by a carriage 70 which also carries the deck 68′ thatsupports the top heater plate 62′ and the top cold plate 66′ of the leftheater tools in FIG. 2. The carriage 70 can be moved in reciprocatingmanner by an actuator 71.

The bottom carriage 60 is carried by a base 72, while the top carriage70 is carried by a carrier plate or beam 74. Said plate or beam isitself supported relative to a reference support plate or beam 76relative to which it can be moved to a small extent vertically. Suchmovement can be achieved by driving an eccentric shaft 78 in rotation(e.g. by means of a rotary actuator (not shown)) whose eccentric iscarried by a bearing 80 that is secured to the plate 74, and whoseportion that is circularly symmetrical about its axis of rotation iscarried by a bearing 82 that is secured to the plate 76. This verticalmovement of the plate 74 makes it possible to move the top heaterplate(s) vertically. They can thus be moved apart to a small extent fromthe top faces of the pellets while said pellets are being advancedthrough one step, and then be moved downwards so that their bottomsurfaces 62A and 62′A come into contact with the top faces of thepellets. Naturally, the top cold plates are moved at the same time.

The reference support plate 76 is itself supported by a stationary plate84 and by an actuator 86, and it can be moved vertically so as to movethe top heater plates away from the bottom heater plates to a largeextent for the purpose of performing maintenance on the machine.

The bottom surface 66A of the top cold plate can be disposed in the samehorizontal plane as the bottom surface 62A of the top heater plate.

In order to make the drawing clearer, the plates 62 and 66 appear to besome distance away from the pellet 12 in FIG. 2. In reality, duringheating, the bottom surface 62A of the plate 62 is in contact with saidpellet, and it is spaced apart therefrom to a small extent while thepellets are advancing. The bottom surface 66A of the plate 66 can be incontact with the pellet or else spaced apart therefrom to a small extentwhile the installation is stopped.

The thickness e of a conveyor slat 46 is advantageously slightly lessthan the thickness E of a pellet prior to thermoforming. This makes itpossible to ensure that both faces of each pellet touch the facingsurfaces of the heater plates, without the slats touching said surfaces.

As can be seen in FIG. 2, the installation includes longitudinal rails88 and 88′ which are suitable for co-operating with the side ends 47 and47′ of the slats while said slats are being driven.

Advantageously, said rails are suitable for supporting the slats whilemaintaining them out of contact with the heater plates. Since the bottomheating plates are stationary, the rails are adjusted so that theysupport the plates so that the bottom faces thereof are very slightlyabove the surfaces of the bottom heater plates, e.g. at a distance ofabout a few a tenths of a millimeter. The difference in thicknessbetween the slats and the pellets also makes it possible to ensure that,even when the top heater plate is in the low position, the slats are notin contact with the bottom surface of said plate.

The rails extend over the entire length of the path along which theslats travel from the inlet table to the outlet of the heater station.

For example, the slats can be made of metal or of a composite material,and they are sufficiently rigid to be capable of being supported viatheir side ends only.

In FIGS. 1 and 3, reference 46F designates the slat that is the lastone, i.e. the one furthest downstream, along the path along which thepellets are conveyed. Said slat 46F is projecting slightly beyond theoutlet of the heater station. The pellet 12D, which is about to bepicked up by the pick-up means so that it can then be disposed in thethermoforming station, is situated between said slat 46F and theconveyor slat 46G that is immediately upstream therefrom.

The pick-up means, constituted, for example, by a suction cup 20, areready to pick up the pellet 12 that is situated between said two slats.The installation includes means for moving the downstream conveyor slat46F away from the upstream conveyor slat 46G before said member picks upsaid pellet. It can be seen that the slat 46F is separated from the slat46G, i.e. that the cell that it forms with said slat for receiving thepellet 12 is opened up. At this time, the pellet 12 is supported by asupport 90. Since the pellet 12 is heated, it can tend to adhereslightly to the concave edges of the slats. The operation consisting inmoving the slat 46F away from the slat 46G tends to unstick said pellet12 from the facing concave edges of said two slats, thereby making iteasier for said pellet to be picked up by the pick-up means 20.

Advantageously, the installation includes means for vertically movingthe pellet 12 that is situated between the slats 46F and 46G towards thepick-up member 20. For example, if, as shown in the drawings, thepick-up member 20 is situated above the pellets, the support 90 that iscarrying the pellet 20 as it exits from the heater station can be thehead of the piston of an actuator 92 which can be moved vertically overa very short stroke. After the slat 46F ahs been moved away, the pistoncan be moved vertically in order further to facilitate unsticking thepellet, and in order to make it easier for it to be picked up by themember 20.

In this example, the means that make it possible to move the slat 46Faway from the slat 46G comprise a separating actuator 94 that takes holdof the slat 46F and moves it away from the slat 46G.

For example, the head of said actuator 94 is formed by a transverse bar96 suitable for being placed above the slat 46F wile said slat is stilldisposed against the slat 46G and is still supported by the rails 88 and88′. Said head 96 carries ratchets 98 that retract when it advances overthe plate 46F and that are deployed naturally, by being urged out bysprings, into bores 100 provided in the slat. When the head 96 moves inthe direction indicated by the arrow F, the slat is thus driven with it.

The slat 46F is thus disposed on a support 102 that forms an elevator.In FIG. 1, said support is shown in uninterrupted lines in its highposition, and in dashed lines in its low position.

The support 102 has two support portions formed by rail segments which,in its high position, come into alignment with respective ones of theabove-mentioned top rails 88 and 88′, and which, when said support is inits low position, come into alignment with respective ones of bottomrails 88 and 88′ that are analogous to the top rails.

When the support 102 reaches its low position, the slat 46F whose bores100 have naturally been released from the ratchets 98, can be pushed bythe head of an actuator 106 in the direction G opposite from thedirection F, so as to be engaged in the bottom rails 88 and 88′.

Thus, by successively pushing the slats 46 that are brought into the lowposition by the support 102, the actuator 106 causes the slats toadvance stepwise over their return path along which they return in thedirection G.

When a slat 46H comes to the end of its return path, under the inlettable 50, it can be separated from the other slats carried by the bottomrails 88 and 88′ by an actuator 108 analogous to the actuator 94 and,like it, provided with ratchets 98. By actuating the actuator 108, saidhead can be caused to advance under the slat 46H, and its ratchetsremain retracted until they reach the bores 100 into which they areurged resiliently. The head of the actuator 108 can then move back inthe direction G while driving the slat 46H with it, said actuator thendisposing said slat on the elevator-forming support 110 which is in itslow position (in uninterrupted lines in FIG. 1) in which its two supportportions formed by rail segments are in alignment with respective onesof the bottom rails 88 and 88′, behind said bottom rails.

The support 110 can then rise into its high position (in dashed lines inFIG. 1) in which its support portions are facing the rear ends of thetop rails 88 and 88′. The slat carried by said support 110 can then bepushed forwards onto the inlet table 50 by the head of the actuator 54.

It should be noted that the head of the actuator 108 passes between thesupport portions of the support 110 so that its ratchets take hold ofthe slat 46H by engaging in the bores therein.

In the example shown diagrammatically, the elevators 102 and 108 arecarried by the moving portions of actuators 104 and 112. Naturally,other systems can be imagined for moving said elevators vertically. Forexample, they can both be connected to a common horizontal shaft via asystem of links that, when said shaft rotates, simultaneously move bothof the elevators, either in phase or in anti-phase.

In a second embodiment shown in FIGS. 8 and 9, the installation includesa bottom belt 500 made of a heat-conducting material. As shown in FIG.8, it is a conveyor belt formed of a loop whose top strand passesthrough the heating station. Its working surface, i.e. its drive topsurface 500B lies substantially in the same plane as the bottom surfacesof the conveyor elements 460.

Thus, the pellets are supported in the heating station 10 by the topsurface 500B of the bottom conveyor belt 500. A stepper motor (not shownherein) makes it possible to cause the belt to advance in a mannersynchronized with the conveyor elements, i.e. the belt accompanies thepellets by advancing stepwise with them so that there is no relativemovement between the pellets and the top surface of the belt. It canthus be understood that the bottom belt 500 constitutes a moving supportfor the pellets 12 while said pellets are passing through the heatingstation 10.

The heating system of the installation further includes bottom heatermeans 520 and means for transmitting the heat generated by the bottomheater means to the bottom conveyor belt 500. Thus, the bottom conveyorbelt transmits to the pellets that are passing through the heatingstation the heat generated by the bottom heater means (which are, forexample, formed by a conventional metal plate that contains heaterresistors).

This bottom plate 520 is situated in the heating station below the drivesurface of the bottom conveyor belt 500 so that the top surface 520B ofthe bottom heater plate is in thermal contact with the bottom surface500A of the conveyor belt 500.

While the heating station is operating, the heat generated by the bottomheater plate 520 is thus transmitted by thermal contact firstly to thebelt 500, and then from said belt to the pellets 12.

To this end, the belt 500 is made of a heat-conducting material andpresents a thickness that is relatively small, e.g. in the approximaterange 2 tenths of a millimeter to 10 tenths of a millimeter. It can thusbe understood that the material of which the belt is made must have verygood physical properties: resistance to traction and to thermaldeformation, and very good heat conductivity while also beingnon-adhesive. In order to satisfy these requirements, an optionallyreinforced composite material is used.

The installation advantageously includes a top belt 600 situated abovethe bottom belt 500 and circulating through the heating station, via thebottom run of the loop that it forms. This top conveyor belt ispositioned such that its drive bottom surface 600A is parallel to thetop surfaces of the pellets that are situated in the heating station 10.

As regards its structure, the conveyor belt 600 can be identical to thebelt 500.

The bottom surface of the belt 600 is suitable for being in contact withthe top surfaces of the pellets 12 that are passing through the heatingstation 10. During normal operation, the bottom surface 600A of the topbelt presses slightly against the top surfaces of the pellets 12 so thatsubstantially no gaps exist between the surface of the belt and the topsurfaces of the pellets.

In the example shown, the heater means include a top heater plate 620placed such that the bottom surface 620A of the said plate is insubstantially gap-free contact with the top surface 600B of the topconveyor belt. Said contact makes it possible to guarantee heatconduction between the heater plate and the belt. The heat is thentransmitted from the conveyor belt to the top surfaces of the pelletswhich are thus heated from their top surfaces.

In addition, the top conveyor belt is driven in a manner synchronizedwith the conveyor belts in the same way as the bottom conveyor belt.This synchronized drive is achieved by means of a stepper motor that isnot shown in the figures.

It can thus be understood that the above-described conveyor belts havetwo functions: to accompany the pellets through the heating station byholding them, and to heat said pellets.

The path followed by the pellets through the heating station isdescribed below.

Upstream from the heating station 10, the installation includes mans 700for depositing the pellets in the cell locations defined by the conveyorelements 460. Said means are in the form of a pick-up mechanism equippedwith a suction cup 480 which takes a pellet from a waiting stock andplaces it in a cell 48 of a conveyor element 460 when said element issituated on an inlet support (not shown in FIG. 9) such as an inlettable disposed between the cog belts described below upstream from thebelt 500, or a portion of belt 500 that extends upstream from the belt600. In this example, each conveyor element is a slat 460 that isprovided with one or more cells, each of which serves to receive onepellet 12. This pellet-depositing operation is performed while the driveis stopped, and, in practice, one pellet is deposited almostsimultaneously in each cell 48 of the slat to be loaded.

The loaded slat is then driven stepwise towards the heating station 10by means of two belts 880, 880′ fixed to the side ends of the slats 460and turning in closed loops. For example, they are cog belts driven bysuitable cog wheels 950. This can be seen clearly in FIG. 9 which showsthe deposition upstream zone of the installation while the installationis stopped.

Advantageously, the conveyor slats 460 present a thickness (e) at themost substantially equal to the thickness (E) presented by the pelletsbefore they are thermoformed, or preferably slightly less than saidthickness (E). Thus, when a conveyor slat 460 containing pellets 12arrives at the inlet of the heating station 10, the bottom and topsurfaces of the pellets are progressively and simultaneously pressedbetween the bottom belt and the top belt. In practice, it is the heaterplates that, in their operating position, press the pellets verticallyvia the belts. Means, e.g. actuators (not shown), are provided formaking it possible to move the heater plates vertically.

In addition, if the heater means are formed by a plurality ofspaced-apart elements (a plurality of heater plates), presser portionspushing the belts against the slats can be disposed between saidelements. However, it can suffice for the deflector rollers 900 fordeflecting the belts, in particular the deflector rollers that aresituated downstream from the heating station, to apply such pressure.

The pellets are heated via the belts as they travel along their paththrough the heating station. The simultaneous action of the heat and ofthe pressure exerted by the belts ensures that the pellets are almost“riveted” into their cells.

While the machine is stopped, the heater plates 520, 620 can be movedvertically away from the belt in order to avoid overheating the pellets.Support rods 980 are disposed under the bottom belt 500 in order to keepit substantially horizontal when the bottom heater plate 520 is in thelow position, as shown in FIG. 10 a. On the top face, the bottom heaterplate is provided with grooves 990 that can receive the rods 980 whenthe bottom heater plate 520 is in the high position as shown in FIG. 10b. It is preferable for said rods 980 to be relatively fine so as toavoid generating non-heated zones on the conveyor belt 500. For example,they are disposed longitudinally under the zones of the slats that aresituated between the cells.

At the outlet of the heater station, the bottom and the top belts reachtheir deflector rollers 900 before the belts that drive the slats reachtheir return cog wheels 950.

Thus, the hot pellets contained in the conveyor slat that reaches theends of the conveyor belts are simultaneously “peeled”, i.e. the contactbetween the surface of the bottom belt and the bottom surfaces of thepellets is broken, and the contact between the surface of the top beltand the top surfaces of the pellets is broken;

The anti-adhesive properties of the material of which the belt is mademake it possible for peeling to take place without damaging or deformingthe hot pellets.

In addition, the above-mentioned “riveting” of the pellets in the cellsin the slats makes it possible to guarantee that the pellets are carriedby the slats in the zone situated between the heating station and theejection station.

The transfer means 18 are analogous to the transfer means of FIG. 1, andthey are in the downstream ejection position as can be seen in FIG. 8.

Advantageously, the installation includes a shaping device disposeddownstream from the heating station and suitable for co-operating withthe peripheries of the pellets 12 before they are thermoformed. As canbe understood with reference to FIGS. 4 to 7, said shaping device isprovided with a support edge 150A and with a shaping clamp 155 whose twoarms, respectively 155A and 155B are suitable for being opened (FIG. 6)while a pellet 12 is being put in place on the support edge 150A, andfor being closed again so as to define between them a shaping outlinefor the pellet.

More precisely, the support edge 150A forms a die-stamping edge of a die150. In this example, the die 150 internally defines a cylinder 158 inwhich the thermoforming piston 24 can move vertically. The die is thusformed directly by the thermoforming countermold.

Prior to die-stamping, the pellet 12 is held on the die-stamping edge150A by being wedged in the shaping outline defined between the arms155A and 155B of the shaping clamp 155. Sometimes, the pellet can beslightly deformed due to it being conveyed through the heating station,and the opening of the arms, shown in FIG. 6, facilitates putting saidpellet in place inside the shaping opening, in spite of any deformation.The shaping clamp is mounted on the die 150 on springs 153. In the freestate, with the die stamp being spaced apart from the die, the shapingclamp is situated in its high position. As can be seen by comparingFIGS. 4 and 5, the die stamp 152 can be moved downwards to co-operatewith the die-stamping edge 150A so as to die-stamp the peripheral region13A of the pellet 12 while said peripheral region is held captive in theshaping device. The periphery of the pellet is held captive in theshaping outline defined by the arms of the clamp 155A and 155B. Underthe effect of the die stamp 152 being moved downwards, the shaping clamp155A is also pushed downwards against the top edge 157 of the setback inthe die 150 in which said clamp is disposed. The setback is defined asbeing set back relative to the die-stamping edge 150A.

It can be seen in FIGS. 6 and 7 that each of the two arms 155A and 155Bof the clamp carries a cam wheel, respectively 156A and 156B. The diestamp 152, which, in this example, is defined by the bottom end of thethermoforming chamber, carries fingers, respectively 157A and 157B whichare carried by the die stamp and which co-operate with said cam wheelsvia their ramps, respectively 157′A and 157′B, to close the arms of theclamp just before the die-stamping proper starts. The arms 155A and 155Bare urged continuously into their spaced-apart position by resilientmeans (not shown), which position is limited by abutments, respectively158A and 158B.

In FIGS. 6 and 7, the shaping device is disposed in the thermoformingstation, and this corresponds to a preferred embodiment. Insofar as thereceptacles are thermoformed upwards, the thermoforming die isconstituted by the top portion of the countermold, while the die stampis constituted by the bottom portion of the mold. Naturally, if thereceptacles were thermoformed downwards, a reverse configuration wouldbe used, the die and the die stamp being constituted respectively by thetop edge of the mold and by the bottom edge of the countermold. In whichcase, the shaping clamp 155 would be carried by the mold.

1. An installation for manufacturing objects such as receptacles bythermoforming pellets of thermoplastic material having top and bottomfaces, said installation including conveyor means for conveying thepellets through stations in the installation, including a heatingstation for heating said pellets, which station includes bottom heatermeans and top heater means, and a thermoforming station for plasticallydeforming the heated pellets by stretching said pellets, the conveyormeans comprising conveyor elements defining cells which are open upwardsand downwards, and each of which is suitable for containing one pelletwhile the entire top and bottom faces of the pellet remain unobstructed,means for depositing the pellets in the cells, drive means for drivingthe conveyor elements through the heating station between the bottomheater means and the top heater means, and transfer means fortransferring the heated pellets to the thermnoforming station, and thebottom heater means operating with a support for the pellets while saidconveyor elements are being driven through the heating station.
 2. Aninstallation according to claim 1, wherein the bottom heater meanscomprise a bottom heater plate constituting a support for the pelletswhile the conveyor elements are being driven through the heatingstation.
 3. An installation according to claim 2, including a coldsupport plate which is disposed on one side of the bottom heater plate,and which has a surface that extends in the same horizontal plane as asurface of said heater plate, the bottom heater plate and the coldsupport plate being mounted to move sideways between a first position inwhich the bottom heater plate is suitable for supporting the pellets anda second position in which the cold support plate is suitable forsupporting the pellets.
 4. An installation according to claim 3,including a cold top plate which is disposed above the cold supportplate, wherein said cold top plate and the top heater means are mountedto move sideways between a first position in which the top heater meansare situated above the pellets and a second position in which the coldtop plate is situated above the pellets.
 5. An installation according toclaim 1, wherein the top heater means comprise a top heater plate thatpresents a bottom surface suitable for being in contact with the topfaces of the pellets.
 6. An installation according to claim 1, includinga bottom belt made of a heat-conducting material, and means fortransmitting heat generated by the bottom heater means to said belt, thebottom belt constituting a support for the pellets which rest on a topsurface of said belt, and the bottom belt being driven through theheating station in a manner synchronized with the conveyor elements. 7.An installation according to claim 6, wherein the bottom heater meanscomprise a bottom heater plate, that presents a top surface in thermalcontact with the bottom surface of the belt, and wherein the bottom beltconstitutes a support for the pellets which rest on a top surface ofsaid belt.
 8. An installation according to claim 6, including a top beltmade of a heat-conducting material, and means for transmitting the heatgenerated by the top heater means to said belt, a bottom surface of saidbelt being suitable for being in contact with the top faces of thepellets, and the top belt being driven through the heating station in amanner such that said belt is synchronized with the conveyor elements.9. (canceled)
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 28. An installation according to claim 7, including a topbelt made of a heat-conducting material, and means for transmitting theheat generated by the top heater means to said belt, a bottom surface ofsaid belt being suitable for being in contact with the top faces of thepellets, and the top belt being driven through the heating station in amanner such that said belt is synchronized with the conveyor elements.29. An installation according to claim 8, wherein the top heater meanscomprise a top heater plate that presents a bottom surface in thermalcontact with a top surface of said belt.
 30. An installation accordingto claim 28, wherein the top heater means comprise a top heater platethat presents a bottom surface in thermal contact with a top surface ofsaid belt.
 31. An installation according to claim 1, wherein theconveyor elements are constituted by conveyor slats presenting athickness at the most substantially equal to a thickness of the pelletsbefore said pellets are thermoformed.
 32. An installation according toclaim 8, wherein the conveyor elements are constituted by conveyor slatspresenting a thickness at the most substantially equal to a thickness ofthe pellets before said pellets are thermoformed and wherein saidinstallation further includes means for pressing the pellets via thebelts.
 33. An installation according to claim 28, wherein the conveyorelements are constituted by conveyor slats presenting a thickness at themost substantially equal to a thickness of the pellets before saidpellets are thermoformed and wherein said installation further includesmeans for pressing the pellets via the belts.
 34. An installationaccording to claim 32, wherein the heater plates press the pellets viathe belts.
 35. An installation according to claim 34, wherein the heaterplates press the pellets via the belts.
 36. An installation according toclaim 6, including support rods for supporting the bottom belt, whichrods are disposed under said bottom belt.
 37. An installation accordingto claim 36, wherein the bottom heater means comprise a bottom heaterplate which, in a top face thereof, is provided with grooves suitablefor receiving the support rods.
 38. An installation according to claim1, wherein the conveyor elements are constituted by conveyor slats, eachcell being defined between an upstream conveyor slat and a downstreamconveyor slat disposed in succession in a direction in which the pelletsare conveyed.
 39. An installation according to claim 38, wherein theoutline of each conveyor slat is provided with a downstream concave edgeand with an upstream concave edge that are mutually aligned in theconveying direction in which the pellets are conveyed, a downstreamconcave edge of a first slat being suitable for defining a cell with anupstream concave edge of a second slat disposed downstream from saidfirst slat.
 40. An installation according to claim 39, including meansfor disposing the pellets in a stack on an inlet table whose surfaceextends in the same horizontal plane as a top surface of the support forthe pellets, wherein the conveyor means include means for bringing aconveyor slat onto the inlet table in a waiting position, said waitingposition being a position in which the downstream concave edge of saidslat is situated facing the stack, and drive means for moving said slatdownstream so that said concave edge co-operates with the bottom pelletin the stack to drive said pellet downstream, at least until said slatcomes into an intermediate position in which the upstream concave edgeof said slat is situated in front of the stack.
 41. An installationaccording to claim 40, wherein the drive means comprise a drive memberthat moves in reciprocating manner between a first position in whichsaid drive member is suitable for co-operating with a slat in thewaiting position and a second position in which said drive member placessaid slat in the intermediate position thereof, and wherein, when a slatreaches the intermediate position thereof, said slat pushes the slatsdisposed in front of it downstream.
 42. An installation according toclaim 1, comprising means for depositing pellets in locations of cellsdefined by conveyor elements on the top surface of an inlet support,during a stop stage, in an upstream region of the heating station. 43.An installation according to claim 1, including rails suitable forsupporting the slats by holding them out of contact with the heaterplates.
 44. An installation according to claim 1, wherein the conveyorelements are constituted by conveyor slats presenting a thickness at themost substantially equal to a thickness of the pellets before saidpellets are thermoformed and wherein said installation includes belts towhich side ends of the slats are fixed, and which drive the slatsthrough the heating station.
 45. An installation according to claim 1,wherein the means for transferring the heated pellets to thethermoforming station comprise a pick-up member, disposed downstreamfrom the heating station and suitable for picking up a pellet that issituated in a cell.
 46. An installation according to claim 38, whereinthe pellet that is picked up is situated between a downstream conveyorslat and an upstream conveyor slat, and wherein the installationincludes means for moving the downstream conveyor slat away from theupstream conveyor slat before said member picks up the pellet.
 47. Aninstallation according to claim 1, including a shaping device disposeddownstream from the heating station and suitable for co-operating withthe peripheries of the pellets before they are thermoformed.
 48. Aninstallation according to claim 47, wherein the shaping device comprisesa support edge and a shaping clamp having two arms suitable for beingopened when a pellet is put in place on the support edge, and for beingclosed again to define between them a shaping outline for the pellet.49. An installation according to claim 48, wherein the support edgeforms a die-stamping edge, and wherein the shaping device furthercomprises a die stamp suitable for co-operating with the die-stampingedge for die-stamping a peripheral region of a pellet while saidperipheral region is held captive in the shaping device.
 50. Aninstallation according to claim 47, wherein the shaping device isdisposed in the thermoforming station.